A CT (computerized tomography) scanner has a large hollow bore into which a patient is inserted longitudinally for imaging. The patient moves generally longitudinally with respect to the scanner (which is typically stationary), and the scanning may be done for a full revolution about the longitudinal axis. No rotation is available for other axes. If need be, the patient can be moved afterwards to a treatment area.
A typical prior art C-arm is a device with an imaging source (e.g., x-ray generator) mounted on one end of the C-arm and an image detector on the other end of the C-arm. The C-arm is a mobile device, and is therefore heavily used in treatment rooms. The construction does not typically allow full axial rotations but provides some limited rotations about a longitudinal axis through the patient (i.e., partial roll) and a vertical axis not through the patient (i.e., partial azimuth).
Imaging devices are also used to assist in target localization in conjunction with treatment equipment having its own rotating gantry, e.g., a linear accelerator (LINAC). However, the imaging device typically moves independently of the gantry of the treatment device. In other words, the coordinate system of the imaging device is separate and independent of the coordinate system of the treatment device. Since localization is required in the treatment device coordinate system, the respective coordinate systems of the imaging and the treatment devices have to be aligned or registered with respect to each other.
An isocentric treatment device, e.g., a linear accelerator, is operable to rotate a treatment head (e.g., a gantry arm with a radiation source disposed therein) having a treatment direction (e.g., the direction of a radiation beam) about a generally horizontal treatment axis (e.g., the longitudinal axis along a patient couch), wherein said treatment direction intersects with said treatment axis at an isocenter. Such an isocentric treatment device may be coupled to a couch operable to rotate (e.g., in azimuth) about a generally vertical couch axis intersecting said isocenter.
An imaging device having an imaging direction (that is, a direction along which an imaging beam is directed) may be added to such an isocentric treatment device for target localization. The imaging device rotates about a generally horizontal imaging axis intersecting with the isocenter. Usually, the treatment axis and the imaging axis coincide, e.g., the imaging device is mounted on the treatment head and rotates with it. However, the prior art has the disadvantage of the imaging axis not being parallel to the couch longitudinal direction for all couch angles.